Fit, cushioning and shock absorption are challenges facing footwear designers. Inflatable articles have been used in the upper, under the foot, or within the sole of a shoe to enhance a shoe's fit, to provide cushioning and to help absorb shock while standing, walking or running. Inflatable products are particularly desirable for footwear because they are lightweight and can be adjustable to accommodate the particular cushioning, support or fit desired by the wearer.
Some inflatable bladders are inflated at the factory, while others have valves fluidly connected to inflation mechanisms, such that the individual wearer may adjust the pressure of the air, or other fluid, within the inflatable bladder. An on-board inflation mechanism, i.e., an inflation mechanism incorporated directly into or onto a shoe, is particularly convenient and allows the wearer to change the pressure within the inflatable bladder without having to carry around a removable inflation mechanism.
Such on-board inflation mechanisms may be accessible to the wearer from the exterior of the shoe, such that the wearer can manually actuate the inflation mechanism when a pressure increase in the shoe is desired. Alternatively, such an on-board inflation mechanism may be positioned beneath a wearer's foot, so that the downward pressure from the foot with each step automatically actuates the inflation mechanism.
Inflatable bladders are typically made of a fluid-tight material such as various thermoplastic materials. However, since air and perspiration do not flow readily through these materials, a wearer's foot may become warm and clammy, creating an excellent environment for harmful bacteria growth. It is therefore desirable to keep a foot cool and dry while in such a shoe.
For example, U.S. Patent Application Publication No. 2004/0003517 discloses a bladder with generally diamond shaped openings therein. The openings are generally made where interior weld lines welding thermoplastic sheets together are formed in a closed diamond shape and the material inside of interior weld line is removed forming an opening. The openings, or windows are particularly useful for allowing air to be accessible to the foot and for allowing moisture to be drawn away from the foot, since synthetic material, such as polyurethane films, may cause the foot to generate moisture in the shoe.
Further, several shoes that automatically try to move air to and from an interior of a shoe have been developed. However, these shoes generally require complex tubing or complex sole designs in order to draw air from one area of the shoe and deliver it to another.